Power module

ABSTRACT

A power module is suggested having a simple and cost-effective arrangement and ensuring a reliable operation. To this end, a circuit arrangement comprising at least one electronic component is arranged on a carrier body. A conductor pattern is formed on the top side of the carrier body, and a structured cooling element made of the material of the carrier body, is provided on the bottom side. The invention also relates to a power module as power converter for electric motors.

FIELD OF THE INVENTION

Electronic modules are used in many areas for different objectives andapplications. Electronic modules constructed as power modules are usedparticularly for control purposes, for example for the closed loopcontrol of the r.p.m. and of the power of electric motors.

BACKGROUND INFORMATION

Electronic components for providing the required power are part of suchpower modules. For example, in connection with electric motors the poweris typically in the kilowatt range. Power modules are used for providingcontrol signals and/or for the evaluation of measured signals. As arule, the active and passive components of the circuit arrangement ofsuch power module require a construction that has a low inductance toavoid excess voltages. Active components include, for example, powercomponents that are working in a switching operation at high speedcurrent changes, particularly integrated switching circuits operating aspower switches. Passive components include, for example resistors, forexample shunts for current measuring, and capacitors. Thus, the circuitarrangement of the power module is customarily applied on an insulatingcarrier body or an insulating substrate consisting as a rule of aceramic material. For mechanical stabilization and for heat dissipationof the dissipation power of the components of the circuit arrangement,particularly the power components, the carrier body is secured to amassive metallic cooling body, for example a copper or an aluminumplate. The carrier body is secured to the cooling body by a bondinglayer, for example by means of solder or a heat conducting paste to forma thermal connection. The insulation or potential separation between theelectronic components of the circuit arrangement and the cooling body isrealized through the insulating carrier body.

The substrate or the carrier body and the cooling body have differentthermal expansion coefficients since the former is made of ceramicmaterial and the latter is made of metal. Therefore, the substrate andthe cooling body have different thermal expansions. As a result, on theone hand, a relatively thick bonding layer is required between thecarrier body and the cooling body, particularly in connection with acarrier body having a large surface for equalizing tensions. The thickbonding layer causes a high heat resistance particularly due toinclusions in the bonding layer such as shrink holes in a solder layer,which negatively influence the heat conductivity. Thus, a poor heattransition exists between the electronic components of the circuitarrangement and the cooling body due to the heat resistances that areformed by the inclusions. As a result, the dissipation of thedissipation power of the electronic components becomes difficult. On theother hand, the connection between the carrier body and the cooling bodyis frequently impaired, whereby the life duration and thus thereliability of the power modules is significantly reduced. This isparticularly true where the power module must work in a largetemperature range and under the temperature changes that such a largerange entails.

OBJECT OF THE INVENTION

It is the object of the invention to provide a power module that has asimple construction and can be easily produced at low cost whileachieving a high reliability and advantageous thermal characteristics.

SUMMARY OF THE INVENTION

This object has been achieved according to the invention in a powermodule that is characterized by the combination of the followingfeatures: a carrier body made of an electrically insulating and heatconducting material, said carrier body having a top surface and a bottomsurface, an electric circuit arrangement including at least oneelectronic component secured to said top surface of said carrier bodyand a conductor structure directly formed on said top surface of saidcarrier body to form said electric circuit arrangement, a plurality offrustum shaped cooling members formed integrally with said bottomsurface and of the same material as said carrier body, said frustumshaped cooling members being arranged in spaced and staggered rowsthereby forming coolant flow channels, each of said frustum shapedcooling members having beveled surfaces slanting away from said bottomsurface so that said coolant flow channels widen away from said bottomsurface for guiding coolant away from said bottom surface for anefficient heat transport.

The following components are particularly provided as parts of the powermodule. A thick carrier body is made of an insulating material which hasa high heat conductivity, which, for example, is made as a ceramiccarrier of a ceramic material such as aluminum oxide Al₂O₃ or aluminumnitride AlN. The carrier body can be produced by drop forging tools, forexample by dry presses or by means of injection casting followed bysintering. The thickness of the carrier body is selected with regard tothe following measures, its size, particularly it surface area, and themechanical loads that are caused by the installation of the power moduleat its point of use, for example by a screw connection and which loadsare further caused by the cooling, for example by the pressure of acoolant in a cooling circuit to which the power module is connected. Astructured partial section of the ceramic carrier body functionssimultaneously as a cooling element wherein geometric cooling membersproject from the bottom of the carrier body to form together the coolingelement. The geometric members are made of the same material as that ofthe carrier body. These geometric members are provided in an array in adetermined arrangement and with a determined geometric form, for examplein the shape of a frustum.

A metallic conductor structure is applied to the top surface of thecarrier body. The conductor structure includes conductor tracks,mounting positions, contact pads, and terminal positions directlyapplied to the surface of the ceramic carrier body that is without anyintermediate layers, for example by active soldering (active metalbonding) in that the conductor structure is chemically soldered directlyto the surface of the carrier body by an oxide bonding or by aDCB-method. The DCB-method involves mechanically anchoring the conductorstructure in the carrier body through the molten metal of the conductorstructure, particularly in the pores of the ceramic carrier body. Theelectronic components of the circuit arrangements are interconnectedthrough the conductor structure with one another and/or with connectorcontacts in an electrically conducting manner.

The electronic components of the circuit arrangement are mounted inrespective mounting positions of the conductor structure, particularlythe power components, for example in the form of silicon chips. Themounting may for example be accomplished with soft solder or bypressing. The silicon chips are contacted with each other and/or withthe conductor structure, for example by means of wire bonds bycontacting the terminals of the electronic components through bond wireswith certain contact pads of the conductor structure or with terminalsof further components. The connection may also be done by a lowtemperature sintering method by a direct application of the terminals ofthe electronic components to one another and sintering. Furthermore,connector contacts are secured to the terminal positions of theconductor structure for the external connection of the power module tofurther structural groups or components.

The heat dissipation of the circuit arrangement or rather thedissipation of the dissipation power of the electronic components of thecircuit arrangement takes place through the structured cooling elementformed of the cooling members on the underside of the carrier body. Thecooling members face away from the bottom surface of the carrier bodyand form its bottom side opposite its top surface. The contour of thecooling element is determined by all cooling members arranged in anarray. The array includes a multitude of similarly structured geometriccooling members which are adapted to the shape of the carrier body. Thesize or surface area of the array depends on the dissipation power thatmust be dissipated. Stated differently, the required cooling functionmust be assured by all geometric cooling members of the cooling array.Accordingly, a certain number of geometric cooling members is arrangedequidistant one behind the other for forming rows and columns. Thegeometric cooling members of two neighboring rows are respectivelystaggered relative to one another, preferably in such a way that thegeometric cooling members of one row are positioned in the gap that isdefined by the spacing of the geometric members of the neighboring rows.

The shape, number and arrangement of the geometric cooling members,particularly the arrangement of the geometric members relative to oneanother and the arrangement of the geometric cooling members in thearray is adapted to the respective purpose of use of the power moduleand to the required cooling power. The geometric cooling members are,for example, shaped as rhombuses, frustums, pegs, or lentils and haveslightly slanted side surfaces. The cooling element with its coolingmembers is produced in the same production step and in the same tool asthe carrier body, for example, in a drop forging tool, or by means ofdry presses or by means of injection molding followed by sintering. Thatmeans, the geometric cooling members that are made of the same materialas the carrier body are removed together with the carrier body from amold having a respective mold pattern. The cooling element with itsarray of the geometric cooling members is particularly integrated into acooling circuit. For example, a coolant such as water or air of thecooling circuit flows through the array. The flow channels for thecoolant of the cooling circuit are formed by the geometric coolingmembers of the array whereby the coolant flows between the geometriccooling members, or rather between the various rows of geometric coolingmembers. The heat transition from the carrier body through the coolingelement to the coolant can be adjusted or adapted by predetermining thearrangement and the structure or shape of the geometric cooling membersand thus of the array.

The power module combines several advantages. The carrier body servesfor the heat dissipation and as a circuit carrier or substrate for theelectronic components of the circuit arrangement. The carrier body alsoserves as a seal when the power module is directly arranged in a coolingcircuit and thus it serves for the integration of the array of thegeometric cooling members into the cooling circuit. By the directmounting of the electronic components of the circuit arrangement on thecarrier body and by the direct connection of the geometric coolingmembers to the carrier body without any intermediate layers a smallthermal resistance is obtained, whereby thermal problems can be avoidedso that a high reliability and useful life of the power module areachieved. By preselecting the structure of the geometric cooling membersa sufficient heat dissipation of the electronic components of thecircuit arrangement is assured, particularly a variably selectable heatdissipation can be achieved by a respective shaping of the geometriccooling members of the cooling element so that particularly inconnection with an integration of the cooling element into the coolingcircuit of a cooling system the through-flow velocity of the coolant andthe pressure loss in the cooling circuit can be adapted to therequirements. The production effort and expense is small because asimple production of the cooling element with its geometric coolingmembers is possible, particularly when the carrier body and thegeometric cooling members are made in a single production step in thesame tool. Thereby, manufacturing problems can be avoided which entailssmall manufacturing costs, particularly also due to the use of simpleand low cost materials.

BRIEF DESCRIPTION OF THE DRAWINGS

The power module will be explained with reference to an exampleembodiment in connection with the accompanying drawings, wherein:

FIG. 1 shows a view of the top side of the power module,

FIG. 2 is a sectional view through the power module, and

FIG. 3 shows a bottom view of the present power module.

DETAILED DESCRIPTION OF PREFERRED EXAMPLE EMBODIMENTS AND OF THE BESTMODE OF THE INVENTION

The power module 1 is for example used as a power converter for liquidcooled electric motors in the field of motor vehicles where a power offor example 10 kW is generated or used. Due to the occurring highdissipation power the power converter 1 is coupled directly to theliquid cooling flow of the electric motor, i.e. it is integrated intothe cooling circuit of the electrical motor whereby a coolant such aswater flows through the cooling circuit.

The power converter 1 comprises a carrier body 2 as a circuit carrierformed, for example as a ceramic substrate or ceramic carrier made of,for example aluminum nitride (AlN). The body 2 has for example thedimensions of 90 mm×57 mm×3 mm. The carrier body 2 is directlyintegrated into the cooling circuit and thus takes over the sealing ofthe cooling circuit relative to the further components of the powerconverter 1.

A conductor structure 7 having a thickness of, for example 0.3 mm isapplied to the top side or surface 14 of the carrier body 2. Theconductor structure 7 is made, for example of copper and includesconductor tracks 8, mounting positions 13, contact pads 9 and terminalpositions 11. The conductor structure 7 is applied to the carrier body2, for example by a direct or active soldering process, or by chemicalsoldering. The electronic components 5 of the circuit arrangement 6 arecontacted at the contact pads 9, i.e. connected in an electricallyconducting manner with the conductor structure 7. Connector contacts 12are secured to the terminal positions 11, for example soldered by meansof solder 20.

A circuit arrangement 6 comprising the electronic components 5 ispositioned on and secured to the carrier body 2. The circuit arrangement6 comprises particularly power components for realizing the converterfunction and the resulting control of the electric motor. The electroniccomponents 5 of the circuit arrangement 6 are silicon chips which aresecured to the mounting positions 13 of the conductor structure 7, forexample by means of a soft soldering process. For example, the chips areconnected through bond connections 10 with the contact positions 9 ofthe conductor tracks 8 of the conductor structure 7 and/or with otherelectronic components 5.

The dissipation power of the electronic components 5 of the circuitarrangement 6, particularly of the power components, is dischargedthrough the carrier body 2 and the cooling element 3 to the coolingcircuit through which the cooling water is flowing. For this purpose thecooling element 3 is arranged on the underside or bottom surface 15 ofthe carrier body 2 opposite the top surface 14. The cooling element 3 isproduced together with the carrier body 2 for example in a drop forgingtool by pressing and is made, for example of aluminum nitride (AlN). Thecooling element 3 is structured in a certain manner for forming an array21 of geometric cooling members 4, whereby the geometric cooling members4 of the cooling element 3, for example have a shape similar to arhombus or frustum. The side surfaces of the shape are slightly beveled.For forming flow channels 18 for the coolant, a certain number of thegeometric cooling members 4 of the cooling element 3 is arranged in arow 17 equidistant one behind the other. The geometric cooling members 4of different neighboring rows 17 are staggered relative to one another.Particularly, two neighboring rows 17 are so staggered that thegeometric cooling members 4 of a row 17 are positioned to face the gapthat is defined by the spacing between the geometric cooling members 4of the neighboring row 17. FIG. 2 shows particularly that, due to thestaggering, edges 4 of the cooling members 4 of one row 17 face the gapbetween two neighboring cooling members of a neighboring row 17 wherebythe coolant is forced to follow a zig-zag flow for an improved surfacecontact between the coolant and the cooling members 4. For example,twelve geometric elements 4 are arranged one behind the other in a row17 along a length of, for example 80 mm. Six different rows 17, forexample are arranged staggered to one another on a width of, for example40 mm. The geometric cooling members 4 of the cooling element 3 projectwith a height of, for example 6 mm into the cooling circuit of theelectric motor and the coolant water flows through the flow channels 18of the cooling element 3. These channels 18 are formed by thearrangement of the geometric cooling members 4 which have the abovementioned beveled surfaces that slant away from the bottom surface 15whereby the coolant flow channels 18 are wider away from the bottomsurface 15 than at the bottom surface. As a result a certain flowdirection and a certain flow velocity of the cooling water ispredetermined or enforced whereby the heat removal efficiency isimproved.

Although the invention has been described with reference to specificexample embodiments, it will be appreciated that it is intended to coverall modifications and equivalents within the scope of the appendedclaims. It should also be understood that the present disclosureincludes all possible combinations of any individual features recited inany of the appended claims.

1. A power module comprising in combination: a carrier body (2) made ofan electrically insulating and heat conducting material, said carrierbody having a top surface (14) and a bottom surface (15), an electriccircuit arrangement (6) including at least one electronic component (5)secured to said top surface (14) of said carrier body (2) and aconductor structure (7) directly formed on said top surface (14) of saidcarrier body to form said electric circuit arrangement (6), a pluralityof frustum shaped cooling members (4) formed integrally with said bottomsurface (15) and of the same material as said carrier body (2), andwherein said frustum shaped cooling members (4) are arranged in spacedand staggered rows (17) thereby forming longitudinal and crosswisecoolant flow channels (18), each of said frustum shaped cooling members(4) having slanted surfaces slanting away from said bottom surface (15)so that said coolant flow channels (18) widen away from said bottomsurface (15) for guiding coolant away from said bottom surface (15) foran efficient heat transport.
 2. The power module of claim 1, whereinsaid spaced and staggered rows (17) of said frustum shaped coolingmembers (4) are arranged in an array.
 3. The power module of claim 1,wherein said frustum shaped cooling members (4) are arranged at an equalspacing from one another.
 4. The power module of claim 1, wherein saidconductor structure (7) arranged on said top surface (14) of the carrierbody (2) comprises conductor tracks (8), mounting positions (13) forholding said at least one electronic component (5) of the circuitarrangement (6), contact pads (9) for contacting the electroniccomponents (5) of the circuit arrangement (6) and terminal positions(11) for the connection of the connector contacts (12).
 5. The powermodule of claim 1, wherein said staggered rows (17) of frustum shapedcooling members (4) are so staggered relative to each other that edges(4′) of said frustum shaped cooling members (4) of one row (17) face arespective gap between two neighboring frustum shaped cooling members(4) in a neighboring row (17) of frustum shaped cooling members.